The present invention relates to methods for attaching polymerizable ceragenins and ceragenin-containing copolymers to polymer substrates; ceragenin-containing copolymers and ceragenin-containing copolymer structures made by these methods; and methods for treating contaminated water using ceragenin-modified treatment membranes and spacers.
Use of ceragenins can minimize or prevent biofouling of filtration membranes used for water treatment and purification. Biofouling (biological fouling) is the undesirable accumulation of microorganisms, plants, algae, etc. on wetted structures. Biofouling, especially microfouling (biofilm formation and bacterial adhesion), impacts membrane separation processes for many industrial applications, such as: desalination, wastewater treatment, oil and gas extraction, and power generation. Biofilms comprise colonies of microorganisms that are attached to a surface and encased in extracellular polymeric substances (aka “slime”). The biofilm is able to trap nutrients for its own growth, and the slime protects the colonies from antibiotics and other anti-microbial agents.
Biofouling of a filtration membrane results in a loss of permeate flux and increase in energy use. For example, in a reverse osmosis (RO) desalination pilot plant using nanofiltration membranes, the normalized pressure drop (actual pressure drop normalized for flow and temperature) increased from about 200 kPa to 400 kPa within a two-week period. Biological analysis of the membranes showed high biofilm densities on the feed side of the spiral wound membrane elements.
The energy sector is concerned about biofouling as water recycling becomes more and more prevalent. Examples include re-use of cooling water, and water used for steam injection for heavy oil extraction. Other sectors that need ultrapure water, such as pharmaceuticals, and the microchip and electronics industries, can also benefit from biofouling resistant membranes.
Traditional methods for preventing biofouling of water treatment membranes include: (1) minimizing microorganisms and nutrients in the feed water and (2) membrane cleaning. Chemical treatment includes the use of silver nanoparticle coatings, chlorine (Cl2) and chlorine dioxide (ClO2) biocides, hydrogen peroxide, and sodium chlorite/hypochlorite. Although oxidizing biocides, such as chlorine, effectively control biogrowth in pipes and filtration membranes, the chlorine significantly damages and degrades RO membranes made of polyamide materials. Silver nanoparticles are expensive, and have other problems.
What is needed is a biocidal material or coating that can be attached onto, or incorporated into, water treatment membranes and/or to spacers that separate adjacent layers of membrane. Ideally, the bacteria are killed before they can colonize, with the dead organisms being swept away by the reject water. The desired biocidal material or coating would have a broad spectrum bactericidal activity, be selectively toxic to prokaryotic cells over eukaryotic cells (e.g., bacteria over human cells), be capable of rapidly killing target organisms, wouldn't allow bacteria to develop a resistance to the biocidal material, and have a long lifetime and low-cost.
Against this background, the present invention was developed.